OhioBob

Kerbal Astronomy 101

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The first time I played Kerbal Space Program, one of the things that I though was a little odd is that we can go to the Tracking Station and immediately zoom in on all the planets and moons and see what they look like. We can also read many precise facts and figures about them. We can do all this before we launch our first rocket.

This got me thinking about what the solar system would look like if we were restricted to Kerbin based observations. How big and bright would the moons and planets be, how much detail could we see through a telescope, what phenomenon could we observe? In other words, what would be the state of pre-space age astronomical knowledge? If we assume that Kerbal and human technology developed along the same or similar path, then Kerbal understanding of their solar system at the start of Year 1 would be much like human understanding of our solar system in the 1950s.

Below is my interpretation of the information that would likely be known to Kerbin-bound observers. Much of the information, such as apparent magnitudes and sizes, is computed from given data. Some of the other information is speculation, but I try to provide the justification for such speculation. Although all the phenomenon that I describe, such as eclipses and transits, would exist in a real solar system, they are not necessarily depicted graphically in the game.

Many facts and figures, such as orbital parameters, would be well known, but other physical characteristics, such as the size and mass of a small and distant body, would be known to much less certainty. I've tried to imply the degree of confidence in a particular value by the number of significant figures use. There are likely some things that Kerbals would be completely wrong about, but I'm not willing to speculate that far.

Sun (Kerbol)

Diameter: 523,000 km
Mass: 1.757×1024 kg
Rotation period: 20 days
Luminosity: 3.161×1024 watts
Surface temperature: 5,840 K (from game files)
Atmosphere: Yes, hydrogen?

The Sun is the dominate body at the center of the solar system. It contains 99.97% of all the mass in the solar system. It has the color and temperature of a G-type main sequence star. However, because of the scaled down size of the Kerbal universe, its luminosity is only 1/18th of what would be expected given its size and temperature. By measuring the value of the solar constant at Kerbin, astronomers can compute the Sun's luminosity. The solar constant is defined in the game's configuration files as 1360 W/m2, from which a luminosity of 3.161×1024 watts is calculated. This would normally imply a surface temperature much cooler than is presumed to be true. It is also presumed that the Sun's radiation peaks in the visible spectrum, as would be the case for a G-type star, rather than in the infrared, as would be the case for a low luminosity star.

The Sun is an average of 13,599,840 km away from Kerbin, a distance that Kerbals define as their astronomical unit, or 1 AU. From this distance the Sun shines at an apparent magnitude of -26.7, the same as Earth's sun. The solar disk in Kerbin's sky subtends an angle of 132 arcminutes, more than four times the apparent angular diameter of Earth's sun.

If Kerbals have come to discover the science of spectroscopy, then they likely have some knowledge of the chemical composition of the Sun. If so, then Kerbals have knowledge that we don't. Chemical composition is something that is undefined in KSP, thus we a left to only speculate about what might exist. Of course it is reasonable to assume Kerbals would figure out that the Sun is composed mostly of hydrogen, just as all stars are.

On the Sun's surface are areas of solar activity that appear relatively dark when seen in white light. These sunspots appear, disappear, and change in shape over time. By following their motion it is determined that the Sun's rotation period is 20 days. (Sunspots may be illustrated as static in the game, but we know in real life they change.)

Moho

Mean distance from Sun: 5,263,000 km
Orbital period: 102.6 days
Diameter: 500 km
Mass: 2.53×1021 kg
Rotation period: 56 days
Albedo: 0.10
Effective temperature: 163 oC
Atmosphere: none
Satellites: none

Although Moho is one of the brighter planets in Kerbin's sky, its closeness to the Sun can make it difficult to observe. At its greatest elongation, Moho is never more than 28o from the Sun. Like the real life planets Mercury and Venus, Moho is seen to pass through phases, appearing full when on the far side of the Sun and a crescent as it nears Kerbin.

The problem with observing Moho is that, at the times when the sky is dark enough to effectively observe it, it is never high above the horizon. This means that it must be observed through a thick and turbulent atmosphere, which degrades a telescope's ability to resolve small details. Moho's disk subtends an angle that varies between 5.2 and 14 arcseconds. When highest in the sky and best positioned for observation, Moho's apparent diameter is about 8". Given this small size and the poor astronomical seeing, it is unlikely that anything more than brightness variations are visible on its surface.

Whether or not visual observations of Moho are of adequate quality to deduce the planet's rotation period is unknown. However, if Kerbal radio astronomy is advanced enough, measuring the Doppler effect of radio waves bounced off its surface can provide this data. It is likely Kerbals know that Moho's rotation is very slow, making less than two rotations every Moho year.

It's possible for astronomers to measure a planet's albedo, the fraction of sunlight that it reflects, from the known amount of sunlight that hits it and the amount they see reflected off of it. We can't do that, but we can compute a planet's brightness if we know its albedo (we'll just pretend that Kerbal astronomers did it the other way around). The albedo of each body is given in the game's configuration files. It's uncertain if the value given is geometric albedo or bond albedo. Geometric albedo is used in brightness calculations and bond albedo in temperature calculations. Since we don't know, we'll assume the same value for both. In Moho's case, its albedo is 0.1.

Moho is at its brightest when full, at which time it can reach an apparent magnitude of -2.4. At greatest elongation it dims to about magnitude -1.3. At this time Moho is bright and conspicuous enough in the evening or morning sky that it was likely known in ancient times.

Knowing the amount of solar radiation Moho receives and its albedo, astronomers can compute its effective temperature, which roughly approximates the global average. Performing these calculations show that Moho is hot, with an effective temperature of 163 oC. Further calculations show that the maximum temperature at the subsolar point should be 360 oC.

Planetary atmospheres can be detected by the dimming of starlight that occurs when a planet's limb occults a star, or by the silhouette the atmosphere produces when the planet transits another body. These techniques would reveal to Kerbal astronomers that Moho has no atmosphere.

Furthermore, the ability of a planet to retain an atmosphere can be computed from its escape velocity and temperature. In KSP, the celestial bodies have been scaled down in size to facilitate better game play, with an apparent scale factor of 0.1 on diameter and 0.01 on mass. To determine the fictionalized ability of a KSP planet to hold onto an atmosphere, we should scale them back up to the size of their real world analog, and then perform the computation on the analog. Doing this for Moho shows that it is too small and too hot to retain an atmosphere of any significance.

The mass of a planet is computed from its gravitational effects. The handiest method is to measure the distance and orbital period of a satellite, then insert these two figures into the proper equation derived from the law of gravitation, which gives the mass of the parent body. Since Moho has no natural satellite, its mass is calculated from the effect of its gravitation on other bodies.

Every so often Moho passes in front of the Sun as seen from Kerbin. During these transits, Moho is visible as a black dot silhouetted against the face of the Sun. These events occur at varying intervals, with a normal of 7 transits occurring every 13-year period.

Eve

Mean distance from Sun: 9,833,000 km
Orbital period: 261.9 days
Diameter: 1,400 km
Mass: 1.224×1023 kg
Rotation period: 22.4 hours
Albedo: 0.45
Effective temperature: 9 oC (atmosphere)
Surface temperature: 135 oC ?
Atmosphere: Yes, carbon dioxide?
Satellites: 1

Eve is the brightest planet in Kerbin's sky. Through a telescope, Eve is seen to pass through phases because its orbit between Kerbin and the Sun makes different amounts of its illuminated hemisphere visible at different times. When full, Eve shines at an apparent magnitude of -3.9. It is brightest when at about a 40% crescent phase, shinning at magnitude -4.9 (the same as Venus at its brightest). Eve comes closer to Kerbin than another other planet. Its disk subtends an angle that varies between 12 and 79 arcseconds. At greatest elongation, Eve is 46o from the Sun and has an apparent diameter of 31".

Eve is the second largest planet by both diameter and mass, with only Jool being larger. Its density is nearly 1.5 times that of Kerbin, easily the highest density among all planets. This suggests that Eve's interior must contain a large core of heavy elements.

Telescopic observations of Eve reveal the presence of a thick atmosphere. However, the question that remains is whether or not there is a thick cloud deck. Eve's albedo is 0.45, which is much higher than expected from its darkly colored surface. This suggests that much of the planet is covered by clouds, even though these clouds are not depicted in the game's graphics. The amount of cloud cover is unknown, but an albedo of 0.45 is on the low end for most cloud types, suggesting that the cloud cover may not be total. It's possible that portions of the surface can be seen through gaps in the cloud layer. Furthermore, radar studies, if sensitive enough, might also reveal some large scale structure. Perhaps Kerbal astronomers have been able to patiently piece together a crude map of Eve's surface.

We know from the game that the molecular mass of Eve's atmosphere is 43 g/mol, suggesting that carbon dioxide is likely the major constituent. It is probable that spectroscopic observation of Eve's atmosphere would find evidence of this carbon dioxide.

Eve's effective temperature is 9 oC, which is a theoretical estimate of the cloud layer temperature, but this tells us nothing about the surface temperature. It's possible that some combination of infrared and/or microwave observations has revealed that Eve has a much hotter surface, resulting from the greenhouse effect. Note that most infrared wavelengths are absorbed by water vapor in the atmosphere. Kerbals can get around this by having their infrared telescopes carried aloft by balloons.

Like Moho, every so often Eve passes in front of the Sun as seen from Kerbin. Transits of Eve are rarer than transits of Moho, with only 6 or 7 events occurring every 75-year period.

Gilly

Mean distance from Eve: 31,500 km
Orbital period: 18 days
Diameter: 26 km
Mass: 2×1017 kg
Rotation period: unknown
Albedo: 0.15
Effective temperature: 40 oC
Atmosphere: none

Eve's moon Gilly is the smallest known moon in the solar system. At its brightest it shines at magnitude +5.0. At most times Gilly is below the threshold at which telescopes can resolve its disk, though at its closest to Kerbin, it can be seen to subtend an angle of 1.5". Estimates place its diameter at about 26 km. Because Gilly's gravitational effects are small, its mass is not well known. The rotation period of Gilly has not been determined. It is theorized that Gilly may be a captured asteroid.

Kerbin

Mean distance from Sun: 13,599,840 km
Orbital period: 426.090 days
Diameter: 1,200 km
Mass: 5.2917×1022 kg
Rotation period: 5h 59m 9.425s
Albedo: 0.35
Effective temperature: -23 oC (atmosphere)
Surface temperature: 13.5 oC average
Atmosphere: Yes, nitrogen/oxygen
Satellites: 2

Kerbin is the third largest planet in the solar system, and the third in distance from the Sun. Its location places it well within the Sun's habitable zone, where temperatures are warm enough for liquid water to exist on its surface. Global temperature extremes vary from 41 oC at the equator, to -35 oC at the poles. The globally averaged temperature is about 13.5 oC.

Kerbin has a thick atmosphere that contains oxygen. The average molecular mass of Kerbin air is approximately 29 g/mol, suggesting that it is likely an earthlike nitrogen-oxygen mixture. Kerbin's albedo is 0.35, which is much higher than expected from the reflectance of its surface. This suggests that cloud cover factors significantly into Kerbin's albedo. Kerbin's effective temperature is -23 oC, indicating that there is a substantial greenhouse effect warming its surface.

Kerbin has no axial tilt and its orbital eccentricity is zero, thus the planet experiences no seasons of any kind. From any specific location on Kerbin, the Sun is seen to follow the same daily path across sky. The entire globe experiences equal periods of daylight and darkness throughout the year. Kerbin's solar day is exactly 6 hours long. The equators of Kerbin and the Sun lie in the same plane, therefore making it possible to use a single celestial coordinate system for bodies orbiting Kerbin and those orbiting the Sun.

Kerbin has two natural satellites, Mun and Minmus. The gravitational interaction of Kerbin and its moons allow the masses of all three bodies to be precisely determined.

Mun

Mean distance from Kerbin: 12,000 km
Orbital period: 6.4345 days
Diameter: 400 km
Mass: 9.760×1020 kg
Rotation period: 6.4345 days
Albedo: 0.10
Effective temperature: -2 oC
Atmosphere: none

Mun is the second largest and brightest body visible from Kerbin, second only to Sun. Its disk subtends an angle of 115 arcminutes, which is nearly four times the apparent diameter of Earth's moon. Like Earth's moon, Mun is seen to pass through phases. At full phase its apparent magnitude is -15.2, or about 10 times brighter than a full moon on Earth.

Assuming Kerbal visual acuity is similar to humans, significant detail can be observed with the naked eye. Through a telescope Mun is observed in stunning detail. It is so close by that, assuming an angular resolution of 1 arcsecond, surface features as small as 55 meters can be resolved. Mun is tidally locked to Kerbin and always keeps the same face pointed toward its parent planet, thus only 50% of its surface is visible from Kerbin. The features of Mun's far side are a mystery.

Because Mun's orbital plane lies within the plane of Kerbin's orbit around the Sun, eclipses are a regular occurrence. Solar eclipses occur every new phase and lunar eclipses every full phase. Because Mun's apparent diameter is smaller than the Sun's, solar eclipses are annular (they can also be called transits). Lunar eclipses, however, are total. One consequence of the unusually perfect orbital alignment is that the central path of solar eclipses is always along Kerbin's equator. Partial solar eclipses are never visible outside of about ±45o latitude of the equator.

Mun's effective temperature is -2 oC, though actual surface temperatures should vary considerably depending on location. The computed temperature of the subsolar point is 120 oC. Observations show that Mun has no atmosphere, as expected based on its temperature and small size.

Minmus

Mean distance from Kerbin: 47,000 km
Orbital period: 49.875 days
Diameter: 120 km
Mass: 2.646×1019 kg
Rotation period: 1.870 days
Albedo: 0.50
Effective temperature: -39 oC
Atmosphere: none

Minmus is the third largest and brightest body visible from Kerbin. Its disk subtends an angle of 8.8 arcminutes, which is about 1/4th the apparent diameter of Earth's moon. Like Mun, Minmus passes through phases. At full phase, its apparent magnitude is -11.4, which is about the brightness of a gibbous moon on Earth.

Minmus' disk is easily resolved with the naked eye. Without optical aid it is likely that a keen-eyed observer can detect albedo variations on Minmus, but probably little else. Through a telescope, Minmus is seen in a resolution similar to viewing its full disk on your computer screen. This is adequate to resolve surface features as small as 225 meters across. Unlike the tidally locked Mun, Minmus has a rapid rotation, thus allowing its entire surface to be seen from Kerbin.

Because Minmus' orbit is inclined to that of Kerbin, solar transits and lunar eclipses are less common than they are for Mun. Minmus lies too far away from Kerbin to experience total lunar eclipses, but Minmus does occasionally pass through Kerbin's penumbra and antumbra shadows. Lunar eclipses and solar transits occur at a frequency that produces an average of 1.5 events of each type per year. Although the frequency is the same, lunar eclipses are routinely visible to a larger population than are transits. This is because they can be seen from anywhere on the nighttime side of Kerbin. Solar transits, on the other hand, are visible only from within a specific path across the globe. Observing a transit may require transportation to a faraway and remote site.

Since Minmus reflects more sunlight than Mun, it has a lower effective temperature of -39 oC. The computed temperature of the subsolar point is 89 oC. Observations show that Minmus has no atmosphere.

Duna

Mean distance from Sun: 20,726,000 km
Orbital period: 1.881 years
Diameter: 640 km
Mass: 4.515×1021 kg
Rotation period: 18.2 hours
Albedo: 0.17
Effective temperature: -58 oC (atmosphere)
Surface temperature: -12 oC daytime ?
Atmosphere: Yes
Satellites: 1

Because Duna is a superior planet, i.e. its orbit lies outside that of Kerbin, it does not pass through phases in the same way as Moho and Eve. Duna is never seen in less than a 76% gibbous phase. Duna is full when it and the Sun are on opposite sides of Kerbin, an alignment called opposition. This is also the time that Duna is closest to Kerbin, reaches its maximum brightness, and can be seen high in the midnight sky. Duna's apparent brightness at opposition varies between magnitude -1.7 and -2.5, depending on Duna's distance from the Sun. Duna's brightness decreases dramatically when not near opposition, dimming to as little as magnitude +1.5 when farthest from Kerbin.

When at its greatest distance from Kerbin, Duna's disk subtends an angle of just 3.7 arcseconds. At opposition, however, Duna's disk grows to a size that subtends an angle of between 16" and 22". The larger apparent size is seen during the more favorable perihelic oppositions, which are those that occur when Duna is near its perihelion. Perihelic oppositions occur about once every 15 years.

Through a telescope, many light and dark markings can be seen on Duna's surface, as well as white polar ice caps. With astronomical seeing limiting resolution to 1" features as small as 30 km can be seen. By following features on its surface, Duna's rotation period of 18.2 hours is precisely measured. Since this period is approximately the length of three Kerbin days, each night Duna will show a face that is about 1/3rd of a rotation different than the night before.

Duna retains a substantial atmosphere. It has an effective temperature of -58 oC, though its surface is likely warmer. We can probably assume that Duna's daytime surface temperatures would be revealed by infrared observations. Duna's albedo is 0.17, which suggests it has little cloud cover.

Ike

Mean distance from Duna: 3,200 km
Orbital period: 18.2 hours
Diameter: 260 km
Mass: 2.78×1020 kg
Rotation period: 18.2 hours
Albedo: 0.14
Effective temperature: -56 oC
Atmosphere: none

Ike is the fifth largest moon in the solar system, but the largest in both diameter and mass when compared to its parent planet. Ike is about 40% of Duna's diameter and 6% of its mass. Ike orbits closer to its parent than any other moon. Duna and Ike are tidally locked to each other, with each keeping the same hemisphere facing the other.

Ike is the only moon beyond Minmus that is commonly visible to the naked eye. At perihelic opposition, Ike shines at magnitude -0.4, which is about 1/7th the brightness of Duna. With Ike and Duna separated by as much as 3.7 arcminutes, it's possible to spot them as separate bodies. One has to wonder if ancient Kerbals would have correctly interpreted the movement of these lights as one body orbiting the other, and what influence this may have had on their early models of the solar system. Humans had to wait for Galileo's telescope before a similar observation could be made.

Through a telescope Ike's disk is seen to subtend an angle that ranges from 1.5" to 8.8". This is large enough to observe light and dark patches on its surface.

The regular movements of Ike result in some interesting events that are visible from Kerbin. A transit occurs when Ike moves across the disk of Duna. A shadow transit occurs when Ike's shadow moves across Duna. An occultation occurs when Duna covers the disk of Ike. And an eclipse occurs when Ike moves into the shadow of Duna.

Dres

Mean distance from Sun: 40,839,000 km
Orbital period: 5.204 years
Diameter: 280 km
Mass: 3.2×1020 kg
Rotation period: 1.6 days ?
Albedo: 0.12
Effective temperature: -118 oC
Atmosphere: none
Satellites: none

Dres is a small planet that varies in apparent brightest from magnitude +6.4 to +3.5. It can be seen with the naked eye during oppositions but is unspectacular. Its disk subtends an angle that ranges from 0.9" to 2.7". Through a telescope it is large enough to be seen as a tiny disk, but too small to observe any surface features. A small brightness fluctuation occurs every 1.6 days, indicating that there may be a patch of lightly color material on its surface that regularly passes into view as the planet rotates. Because Dres' gravitational effects are so small, its mass is not well known.

Jool

Mean distance from Sun: 68,774,000 km
Orbital period: 11.37 years
Diameter: 12,000 km
Mass: 4.233×1024 kg
Rotation period: 1.67 days
Albedo: 0.52
Effective temperature: -170 oC
Cloud temperature: -100 oC ?
Atmosphere: Yes, hydrogen?
Satellites: 5

Jool is by far the solar system's largest planet. Its mass is more than 16 times the mass of all other planets and moons combined. Its diameter is ten times Kerbin's diameter. Despite its great size, Jool is significantly less dense than the other planets. This suggests that it has an entirely different internal structure, consisting not of rock and metals, but of highly compressed lighter elements. The term gas giant has been coined to describe Jool-type planets.

Despite its great distance from Kerbin, Jool is so large that its disk subtends an angle of 29" when farthest away and 48" when closest. Jool's size and high albedo makes it the second brightest planet in Kerbin's sky. Jool's apparent magnitude ranges from -1.6 to -3.0.

When viewed through a telescope, all that can be seen of Jool is an impenetrable veil of clouds. This cloud surface is green in color with varying light and dark shades forming horizontal bands and swirls. If Jool has a solid surface, it is presumed to be deep beneath the thick atmosphere. Jool's effective temperature is -170 oC, though astronomers may learn through infrared studies that its cloud layer is considerably warmer. The higher than expected temperature would suggest that Jool emits heat of its own.

Of considerable interest when observing Jool is its family of moons. There are five in total, listed in order of distance from Jool: Laythe, Vall, Tylo, Bop and Pol. The three innermost are large enough to be planets in their own right. All three are bright enough to be seen with the naked eye, though their closeness to the much brighter Jool makes this very difficult. When observing these moons through a telescope, one can frequently see transits, shadow transits, occultations, and eclipses.

Laythe

Mean distance from Jool: 27,000 km
Orbital period: 2.45 days
Diameter: 1,000 km
Mass: 2.94×1022 kg
Rotation period: 2.45 days
Albedo: 0.3
Effective temperature: -160 oC
Surface temperature: >0 oC ?
Atmosphere: Yes

Laythe is Jool's closet and second largest satellite. It is comparable in size to Kerbin, having 83% of Kerbin's diameter and 56% of its mass. As seen from Kerbin, Laythe's apparent magnitude varies between +4.4 and +3.0. Its disk subtends an angle that ranges from 2.4" to 4.0". Laythe is in orbital resonance with Jool's second and third moons, Vall and Tylo. The three moons orbit in a 4:2:1 resonance.

Because of its small apparent size and lack of large-scale surface variation, a telescopic view of Laythe probably appears rather featureless. However, this doesn't mean that astronomers are clueless about its surface composition. Different surfaces (soil, ice, water, vegetation, etc.) have different spectral reflectance signatures. Since Laythe is almost completely covered by a global ocean, it's possible that Kerbals would detect evidence of this liquid surface in the light that it reflects. It should also be noted that Laythe's albedo of 0.3 suggests that clouds contribute significantly.

The presence of liquid on Laythe's surface requires a substantial atmosphere and sufficiently warm temperatures. Observations would confirm the existence of the atmosphere, but Laythe's effective temperature is only -160 oC. If the liquid on the surface is water, then Laythe requires a source of internal heat, possibly generated by tidal heating. Laythe is undoubtedly the subject of much discussion among Kerbal planetary scientists.

Vall

Mean distance from Jool: 43,000 km
Orbital period: 4.91 days
Diameter: 600 km
Mass: 3.11×1021 kg
Rotation period: 4.91 days
Albedo: 0.5
Effective temperature: -169 oC
Atmosphere: none

Vall is Jool's second moon by distance and third by size. From Kerbin, Vall's apparent magnitude varies between +4.9 and +3.6. Its disk subtends an angle that ranges from 1.4" to 2.4". Through a telescope, Vall appears as a tiny featureless disk.

Vall's high albedo and low density differentiates it from Laythe and Tylo, and suggests that Vall is likely composed of a substantial amount of ice. If Vall's interior is tidally heated, it may contain subsurface liquid water. Vall shows no evidence of an atmosphere. Calculations show, however, that Vall is capable of retaining at least some atmosphere. Its close proximity to massive Jool means that Vall is almost certainly tidally locked.

Tylo

Mean distance from Jool: 68,500 km
Orbital period: 9.81 days
Diameter: 1,200 km
Mass: 4.23×1022 kg
Rotation period: 9.81 days
Albedo: 0.1
Effective temperature: -153 oC
Atmosphere: none

Tylo is the largest satellite in not only the Joolean system, but the entire the solar system. Its diameter is equal to Kerbin, but it has only 80% of Kerbin's mass. From Kerbin, Tylo varies in apparent brightness from magnitude +5.1 to +3.8. Its disk subtends an angle that ranges from 2.9" to 4.8".

Close up views of Tylo shows what appears to be small variations in surface brightness between its eastern and western hemispheres. It might be possible for astronomers on Kerbin to detect these very slight changes as the planet rotates. If so, following these variations would confirm that Tylo's rotation is tidally locked to Jool. Tylo is certainly large enough to retain a substantial atmosphere, but none has been detected. It is the largest solar system body not to have an atmosphere.

Bop

Mean distance from Jool: 128,500 km
Orbital period: 25.2 days
Diameter: 120 km ?
Mass: 3×1019 kg ?
Rotation period: 25.2 days ?
Albedo: 0.25 ?
Effective temperature: -160 oC ?
Atmosphere: none

Bop, the fourth moon of Jool, is in a highly eccentric and inclined orbit. Its maximum brightness at opposition is magnitude +7.9. Bop is too small for telescopes to resolve its disk. It is assumed to be tidally locked to Jool.

From its measured brightness and small gravitational effects, astronomers can make a best guess estimate of Bop's diameter and mass. Furthermore, stellar occultations by Bop can provide additional information about its size, though these events happen rarely. The characteristics listed above are a fictionalized example of the type of uncertain numbers that astronomers might derive.

Pol

Mean distance from Jool: 180,000 km
Orbital period: 41.8 days
Diameter: 100 km ?
Mass: 2×1019 kg ?
Rotation period: 41.8 days ?
Albedo: 0.4 ?
Effective temperature: -160 oC ?
Atmosphere: none

Pol, the farthest moon of Jool, is in a moderately eccentric and inclined orbit. Its maximum brightness at opposition is magnitude +7.8. Pol is too small for telescopes to resolve its disk. Like Bop, Pol's size and mass are estimated from its brightness and small gravitational effects. Pol is assumed to be tidally locked to Jool. It is believed that Pol and Bop may be captured asteroids.

Eeloo

Mean distance from Sun: 90,119,000 km
Orbital period: 17.06 years
Diameter: 400 km
Mass: 1×1021 kg
Rotation period: unknown
Albedo: 0.5
Effective temperature: -182 oC
Atmosphere: unlikely
Satellites: none

Among the orbits of the seven planets, Eeloo's is the largest, most eccentric, and second most inclined. The orbit is so eccentric that Eeloo's perihelion lies inside the orbit of Jool. As seen from Kerbin, Eeloo's apparent brightest varies from magnitude +7.5 at its farthest to +4.5 at its closest. Eeloo's disk subtends an angle of between 0.7" and 1.6".

When near its closest distance to Kerbin, Eeloo can be spotted with the naked eye. Through a telescope it can be resolved into a tiny disk. Eeloo shows no features or brightness variations, thus its rotation period is unknown. Eeloo has no known satellites and its gravitational effects are very small, thus its mass is not well known. Eeloo's composition likely includes a substantial amount of ice.

Eeloo's distance from the Sun and high albedo makes it the coldest place in the solar system. Its effective temperature varies between -167 oC at perihelion and -192 oC at aphelion. No atmosphere has been detected but, because of the very cold temperatures, the possibility of a thin atmosphere has not been completely ruled out.

Imagery

As a final exercise I Photoshopped some images that depict what I think the moons and planets would look like from Kerbin. I sized the images so that the image resolution matches normal naked eye or telescopic resolution. For example, naked eye resolution is typically 1 arcminute, so Mun, which has an angular size of 115 arcminutes, was sized to be 115 pixels across. For telescopic views the resolution is 1 arcsecond. Of course it is possible to increase magnification, but this won't increase resolution. You'll just get a bigger and fuzzier image, much as would happen if you simply zoomed in on the images below.

Composite.png

Edited by OhioBob

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Awesome work Bob! I was wishing I had a data-base like this! For my part, this is Greatly appreciated. This falls right in line to how I first approached playing the game.

I have printed this out, and will relish absorbing this when I get home from work! Thank you.

- In fact, if this game had a manual, THIS would be in it.

Edited by GarrisonChisholm

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Im going to need to go back and read the rest of that later. Thats incredible. I just want to say real quick. That KSP actually needs to emulate this imo. Or a mod. A... "Fog of Distance" mod if you will. That in order to SEE the planets in the tracking station/map you need to gather visual data. Planets should just start out as flat, blurred blotches in the tracking station and maps view or not even exist until you look at them through a telescope.

And to take it a step further what you see in the tracking station/map view consists only of what you've personally seen so far. So if through a telescope you've only seen half of Eve then thats all you get. The other side is still blurred out. And the view you do have wouldn’t be full resolution until you've flown by and with your own eyes have seen the planet. And to take it even another step further. Tie it into the science system with required cameras. And only what those cameras capture is recorded into the map/tracking station views.

For instance the far side of the Mun. Shoud be a complete blank until you send something there.

Edited by Motokid600

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This is awesome! +rep indeed.

I can't see any images, though. Can you post it on imgur?

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I just want to say real quick. That KSP actually needs to emulate this imo. Or a mod. A... "Fog of Distance" mod if you will. That in order to SEE the planets in the tracking station/map you need to gather visual data. Planets should just start out as flat, blurred blotches in the tracking station and maps view or not even exist until you look at them through a telescope.

And to take it a step further what you see in the tracking station/map view consists only of what you've personally seen so far. So if through a telescope you've only seen half of Eve then thats all you get. The other side is still blurred out. And the view you do have wouldn’t be full resolution until you've flown by and with your own eyes have seen the planet. And to take it even another step further. Tie it into the science system with required cameras. And only what those cameras capture is recorded into the map/tracking station views.

For instance the far side of the Mun. Shoud be a complete blank until you send something there.

I had the same thought. I think it would make the game seem more real if we had to go out and discover these things rather than have them handed to us right from the start. It might make it feel like we were doing real sicence rather than just collecting points. It might also be interesting if some of the properties of the planets/moons were randomized so that each game were a little different with unknowns that would have to be discovered. Perhaps as an option: play with standard planets, or play with randomized planets.

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I can't see any images, though. Can you post it on imgur?

I don't know, I've never used imgur. I'll have to check it out.

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I really want this as a little hardcover reference book with pretty pictures and diagrams and glossy pages :)

.........................kickstarter?

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would you consider doing this for the Outer Planets mod as well? They added quite a few.

I'm not familiar with that mod. I'll have to investigate.

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I love your idea. I had always understood that there would be some form of discovery mechanic. But completely support this.

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I really want this as a little hardcover reference book with pretty pictures and diagrams and glossy pages :)

.........................kickstarter?

I would totally support this and would buy a copy. It could be published as an unofficial strategy guide and if you do it right, you can ensure you don't run afoul of intellectual property laws. http://www.avvo.com/legal-answers/written-walkthrough-or-strategy-guide-for-video-ga-1336565.html

It would be even better if Squad reached out to OhioBob and worked out a deal to include this in the official game.

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I would totally support this and would buy a copy. It could be published as an unofficial strategy guide and if you do it right, you can ensure you don't run afoul of intellectual property laws.

It would be even better if Squad reached out to OhioBob and worked out a deal to include this in the official game.

If anything like that were to happen, I would want to write it in a different style. What I wrote in this thread is just an interpretation of given facts, along with a little bit of speculation surrounding some "what if" questions. I purposely tried not to make any creative decisions. If I were to write something more formal, I'd want to put it into the style of a fictionalize astronomy book and exercise some creative freedom. For example, instead of speculating about what Kerbals might know if they have spectroscopy, I would want the creative freedom to say that Kerbals do (or do not) have spectroscopy and this is what they do know (or at least what they think they know). I think it might also be interesting to alter some of the "facts" just a bit to show how uncertain their pre-space age understanding is. For example, if you were to read a 60 year ago astronomy book, you'd see that we were wrong about some things. Of course, writing in this way means that I'd be introducing some new fiction to the story that didn't come from Squad, but I think it would be more entertaining to read.

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If anything like that were to happen, I would want to write it in a different style. What I wrote in this thread is just an interpretation of given facts, along with a little bit of speculation surrounding some "what if" questions. I purposely tried not to make any creative decisions. If I were to write something more formal, I'd want to put it into the style of a fictionalize astronomy book and exercise some creative freedom. For example, instead of speculating about what Kerbals might know if they have spectroscopy, I would want the creative freedom to say that Kerbals do (or do not) have spectroscopy and this is what they do know (or at least what they think they know). I think it might also be interesting to alter some of the "facts" just a bit to show how uncertain their pre-space age understanding is. For example, if you were to read a 60 year ago astronomy book, you'd see that we were wrong about some things. Of course, writing in this way means that I'd be introducing some new fiction to the story that didn't come from Squad, but I think it would be more entertaining to read.

I was definitely thinking along the lines of "interesting read and nifty coffee table book made to look like a legitimate reference text" rather than actual reference...

I could see this sort of thing turning into a big community project, I'm sure people would love it :)

I was also thinking of a pre, and post space-age version... The post would obviously be written in the Kerbal style of "The surface of Minmus might look appetizing to most, but it is in fact NOT a snack, composed of mostly XXXX with trace amounts of XXXX and XXXX, enough to give even the hungriest Kerbal a stomach-ache. For centuries, astronomers had formulated many theories around the apparent edible nature of the small moon, but advances in technology have finally put this ancient folklore to rest. You can still find some niche groups of crack-pot theorists who believe that the Kerbal Space Program will one day open an all-you-can-eat dessert buffet on the surface of Minmus."

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The post would obviously be written in the Kerbal style of "The surface of Minmus might look appetizing to most, but it is in fact NOT a snack, composed of mostly XXXX with trace amounts of XXXX and XXXX, enough to give even the hungriest Kerbal a stomach-ache. For centuries, astronomers had formulated many theories around the apparent edible nature of the small moon, but advances in technology have finally put this ancient folklore to rest. You can still find some niche groups of crack-pot theorists who believe that the Kerbal Space Program will one day open an all-you-can-eat dessert buffet on the surface of Minmus."

I like it, but that style of writing is something I'd have trouble with. I'm not that creative with language. My style is better suited to a astronomy textbook. Of course that is one of the advantages of possibly turning it into a community project, different people can contribute in different ways.

I also like the idea pre and post space age versions. The pre-version would be really lacking in photos (there are only so many fuzzy telescopic pics that could be included), but most of the old astronomy books that I've seen were illustrated with artist impressions. If we don't have any artists, Photoshop has some filters that could possibly take some screenshots and make them look like artist illustrations. The post-version could be chock-full of "photos" (screenshots actually).

I might take what I have already done and see if I can turn into more of a book format. There is certain quite a bit of information that I can add to it. If I'm able to come up with a sample, I can make it available as a PDF.

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I second the inability to see any of the pictures you mentioned. Can you at least squeeze in a link?

Here's the link, maybe this will work better

http://www.braeunig.us/pics/KSP/Composite.png

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Now if we only had a place for stuff like this, something like wiki...

I've made contributions to the Wiki, but in this case I'm not sure it is appropriate. The Wiki seems to limit itself to things that are actually in the game. To say something like "at perihelic oppostion Duna shines at magnitude -2.5 and subtends and angle of 22 arcseconds" is just hypothetical and is not something that is depicted in the game or that can be experienced while playing the game. If enough other people think that it is appropriate to include this type of information in the Wiki, then perhaps I'll consider adding it.

Edited by OhioBob

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I like the idea of adding this dynamic to the game!

I'm not sure how it would work in the early going with the ability to click on different bodies, but it would be awesome if info from probes helped to fill in the blanks. Of course, this would mean that scanning sensors would need to be moved up the tech ladder...

Or conversely a manned pod would act as a low- res surface scanner for topo info, but the bitmap doesn't show up in the science complex or tracking station until either the kerbonaut is recovered or the data is transmitted.

Best,

-Slashy

Edited by GoSlash27

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Your image link appears to be questionable.

gy3Syoy.png

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Forgot to include this...

www.braeunig.us uses an invalid security certificate. The certificate is only valid for the following names: *.securedata.net, securedata.net (Error code: ssl_error_bad_cert_domain)

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Your image link appears to be questionable.

Well that's disheartening. I've never seen or heard of this before. Sounds like I may need to contact my website host.

Can you access my web page, in signature below?

Edited by OhioBob

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Fantastic work, OhioBob! (I'd rep you but apparently I have done so too recently.)

I would love for map mode to become a proper map with info that fills in as it is discovered, it would make doing actual science and things like telescopes and probes more worthwhile.

I clicked through the security warning and saw the pic just fine, fwiw.

Edit: Using http instead of https fixes it: http://www.braeunig.us/pics/KSP/Composite.png

Edited by Red Iron Crown

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Well that's disheartening. I've never seen or heard of this before. Sounds like I may need to contant my website host.

Can you access my web page, in signature below?

Yes, no problem opening that. Nice page by the way.

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Ah, thanks. I've edited everything to make it http. I didn't even notice that I used https, which was my mistake.

You should fix your HTTPS certificate though. It's generally better to encrypt by default, and valid certificates are free (through StartSSL, soon through Let's Encrypt).

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